The proposed study will attempt to identify some mechanisms of fetal intrauterine growth. As a model for successful intrauterine growth, the study will focus on the macrosomic infant. This infant is most commonly the product of a diabetic mother, a mother with gestational carbohydrate intolerance, obesity, or from a mother with previous history of delivery of a macrosomic infant. Complications of macrosomia include birth trauma, cesarean section, and hypoglycemia. Infants of diabetic mothers are also at risk for respiratory distress syndrome and congenital anomalies. This study will attempt to identify those mechanisms that contribute to excessive intrauterine growth and to formulate reasonable antenatal predictors of excessive fetal growth at an early stage in pregnancy, when dietary or medical intervention may be effective in reducing fetal and maternal morbidity. The study population will be drawn from a study designed to identify women at risk for carbohydrate intolerance during pregnancy, obesity, of delivery of a macrosomic infant. Results of dietary and medical intervention will be evaluated and correlated with hormonal contributions to macrosomia. Maternal and fetal concentrations of insulin, C-peptide, insulin-like growth factors I and II, human chorionic gonadotropin, human placental lactogen, and cord blood concentrations of growth hormone and erythropoetin will be measured. Hormone concentrations will be correlated with anthropometirc data obtained from infants. In vitro studies of interaction insulin and insulin-like growth factor at the cellular level will be done to determine the contribution of each to fetal macrosomia. The overall goals of this study are 1) to reduce maternal and fetal morbidity in the diabetic and gestational diabetic pregnancy through early identification of patients at risk, improved dietary control, and medical management 2) to develop an understanding of hormonal mechanisms acting on fetal growth, and 3) to develop predictive indices for excessive fetal growth at an early stage of pregnancy which allows for improved management and reduced maternal and infant morbidity.